185/70R18 vs 195/65R18
Going from one to the other changes the overall height by -0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/70R18 | 195/65R18 | Change |
|---|---|---|---|
| Overall height | 28.2" | 28.0" | -0.8 % |
| Sidewall | 5.10" | 4.99" | -2.1 % |
| Section width | 185 mm | 195 mm | +5.4 % |
| Circumference | 88.6" | 87.9" | -0.8 % |
| Revs per mile | 715 | 721 | +0.8 % |
| Axle height | 14.10" | 13.99" | -2.8 mm |
| Approved rim width | 5–6.5" | 5.5–7" | overlap 5.5–6.5" |
Both are approved on a rim 5.5" to 6.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 185/70R18. Fit 195/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.5 mph | -0.5 |
| 90 mph | 89.3 mph | -0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,923 on the road, so it over-counts by 77. At a true 70 mph the first turns 834 times a minute, the second 841.